1. Field of the Invention
The present invention relates to an ink jet recording material and a process for producing the same. More particularly, the present invention relates to an ink jet recording material having excellent gloss, ink-receiving property, water-resistance, weather resistance and being capable of recording ink images with excellent color density and brightness and clarity, and a process for producing the same.
2. Description of the Related Art
The ink jet recording system is an ink image recording system wherein ink droplets are jetted through an ink-jetting nozzle toward a recording material and jetted ink droplets are absorbed in and fixed on the recording material, to form ink images. This ink jet recording system is advantageous in that full colored images can be easily formed and the printing noise is low.
The ink usable for the ink jet recording system contains a large amount of a solvent in which a coloring material is dissolved or dispersed and thus, to obtain a high color density of the recorded ink images, a large amount of the ink must be absorbed in the recording material. In the complete absorption of the ink droplets reached the recording material, a certain length of time is necessary. This feature of the ink jet recording system causes such a disadvantage that when the ink droplets are continuously jetted imagewise to form ink dots on the recording material surface, sometimes the ink droplets reach a target dot before an ink dot adjacent to the target dot has been completely absorbed in the recording material, and the target ink dot is connected to the adjacent ink dot so that the resultant ink image becomes unclear.
Accordingly, if the recording material for the ink jet recording system is to have such an advantage that the ink dots formed thereon have high color density and brightness and a high clarity, the ink droplets must be rapidly absorbed therein and even if the ink dots are overlapped on each other, substantially no blotting of the ink may occur.
When a coated paper sheet is used as a substrate for the ink jet recording material, at least one ink-receiving layer comprising a porous pigment is formed on the coated paper sheet to control the color brightness and sharpness of the ink images from which the image quality is established and to enhance the color-reproducibility and image-reproductivity. For example, Japanese Unexamined Patent Publication No. 62-111,782, No. 63-13,776 and No. 63-104,878 disclose an ink jet recording sheet having an ink-receiving layer containing primary or secondary pigment particles (usually, silica or alumina particles) having fine pores, and a binder. Also, Japanese Examined Patent Publication No. 63-22,977 discloses an ink jet recording sheet which has an ink-receiving layer including an uppermost layer provided with pores having a peak size of from 0.2 to 10 xcexcm, and is capable of receiving an absorbed ink in voids having a size of 0.05 xcexcm or less, and of forming ink images with a high quality.
Currently, due to the rapid spread of ink jet printers, various ink jet prints with a high gloss similar to that of photographic prints are demanded for publications and packing paper sheets. Particularly, in colored prints, film type or coated sheet type ink jet recording sheets which have high ink-absorbing and fixing rates and a high ink absorption are in great demand. To provide the above-mentioned ink-receiving layer having an increased porosity, it is necessary to use pigment particles having an increased particle size in the xcexcm order or to utilize secondary particles of pigment. When the size of the pigment particles is increased, the resultant ink-receiving layer exhibits a decreased smoothness and a reduced light transmission. Namely, the resultant ink-receiving layer is opaque and has a poor gloss.
Various types of ink jet recording sheets having an ink-receiving layer containing a resin capable of dissolving therein the ink and of swelling by the ink are practically used. These types of ink jet recording sheets have an enhanced gloss. However, they are disadvantageous in that the resultant ink-receiving layer exhibits a low ink-drying rate and unsatisfactory resistance to moisture and water.
To enhance the smoothness and gloss of the ink-receiving layer, it has been attempted to form the ink-receiving layer in a two or more layered structure wherein an uppermost layer has a high gloss. This type of ink jet recording sheet is disclosed in, for example, Japanese Unexamined Patent Publications No. 3-215,080, No. 3-256,785, No. 7-89,220, 7-101,142 and 7-117,335. In this type of ink jet recording sheet, colloidal particles or a complex of colloidal particles are commonly used as a principal component of the high gloss layer. This type of high gloss layer is formed from the colloidal particles or complex thereof dispersed in a binder comprising a polymer latex, to establish a satisfactory transparency and ink-absorption. When the polymer latex is used as a binder, a plurality of small cracks are formed in the resultant coating layer. The small cracks are contributory to enhancing the ink-absorption of the ink-receiving layer. However, the small cracks cause the resultant ink dots formed on the cracked ink-receiving layer to have jagged circumferences significantly different from round circumferences, and thus the resultant ink images to exhibit reduced clarity and sharpness. Also, the small cracks cause the printed ink to spread on the ink-receiving layer and thus the ink dots to be enlarged. When the ink dots are formed in a usual density of the level of 360 dots per inchxc3x97360 dots per inch (dpi), the spread of the ink dots due to the small cracks of the ink-receiving layer does not cause any problems. However, if the ink dots are formed in a high density of the level of 720 dots per inchxc3x97720 dots per inch or more, the spread of the ink causes the spread ink dots to be connected to each other and thus the resultant ink images exhibits significantly reduced clarity and sharpness. Also, the colloidal particles in the uppermost high-gloss layer are primary particles and thus have substantially no fine pores capable of receiving the ink therein. Therefore, the ink is absorbed in the ink-fixing layer formed under the uppermost high-gloss layer. In the above-mentioned multi-layered ink-receiving layer, an ink-fixing layer is formed under the high gloss layer, and the thickness of the ink-fixing layer is larger than that of the high gloss layer. Also, the ink-fixing layer contains secondary particles of a pigment having a particle size in a xcexcm order, the resultant multi-layered ink-receiving layer exhibits a significantly reduced transparency and thus the ink images fixed in the ink-receiving layer exhibit an unsatisfactory color density. Especially, this type of ink-receiving layer exhibits a reduced light reflection and thus an insufficient gloss.
To prevent the formation of the small cracks in the ink-receiving layer, Japanese Unexamined Patent Publication No. 7-117,334 provides an ink-receiving layer formed from a composition comprising pigment particles with a particle size of 0.1 xcexcm or less and a polyvinyl alcohol with a degree of polymerization of 4,000 or more. The pigment particles are selected from primary pigment particles for example, colloidal silica or alumina sol. Therefore, in the resultant ink-receiving layer, the ink absorption and the transparency are unbalanced. Namely, since the pigment primary particles per se have no ink-absorption, the ink is absorbed in the gaps between the pigment primary particles. The gaps between the pigment primary particles in the ink-receiving layer are filled by a film-forming binder which is necessary to bond the pigment particles and to form an ink receiving layer. Therefore, the binder-filled gaps between the pigment particles exhibit a low ink absorption. To completely absorb a large amount of the ink, the ink-receiving layer must be formed in a large thickness. The ink-receiving layer with a large thickness easily forms small cracks. Also, to obtain an ink-receiving layer having a high transparency, the pigment primary particles must be selected from those having a small particle size.
The smaller the pigment primary particle size, the lower the ink-absorbing rate of the resultant ink-receiving layer. However, the larger the pigment primary particle size, the lower the transparency of the resultant ink-receiving layer, and the lower the color density of the printed ink images.
Japanese Unexamined Patent Publication No. 2-276,670 discloses an ink-receiving layer for an ink jet recording material. The ink-receiving layer is formed from a mixture of pseudoboehmite and a binder and has a plurality of pores having a radius of 40 to 100 angstrom (4 to 10 nm) and a total volume of 0.1 to 0.4 ml/g. The pseudoboehmite particles affect the hue of a certain type of inks which are affected by alumina. Accordingly, the pseudoboehmite-containing ink-receiving layer is unsuitable for the above-mentioned inks, for example, Acid Red 52 (food red dye No. 106). Also, the pseudoboehmite has a disadvantage in that it per se is yellowed with a lapse of time. Further, the pseudoboehmite is expensive and thus is difficult to use in practice. Furthermore, the pseudoboehmite particles are colloidal primary particles having a poor ink absorption and thus the resultant ink-receiving layer has an insufficient total pore volume and exhibits an unsatisfactory ink-absorbing rate and ink-absorption capacity.
Japanese Unexamined Patent Publications No. 5-32,037 and No. 6-199,034 disclose an ink jet recording material having an ink-receiving layer which contains agglomerated secondary particles of pseudoboehmite with a particle size of 100 to 500 nm and is provided with pores having a radius controlled to 30 to 100 angstrom (3 to 10 nm). However, this ink-receiving layer contains the pseudoboehmite particles and thus can not be released from the disadvantages derived from the pseudoboehmite particles. Namely, although the agglomerated secondary particles of pseudoboehmite are contributory to enhance the ink absorption of the resultant ink-receiving layer to a certain extent, the total pore volume of the ink-receiving layer containing the agglomerated secondary particles of pseudoboehmite is not sufficiently large and thus when the ink dots are formed in a high density of 720 dipxc3x97720 dpi or more, the ink-receiving layer does not completely absorb the ink at a satisfactory ink-absorbing rate.
Japanese Unexamined Patent Publication No. 7-117,335 discloses an ink jet recording material having an ink-receiving layer having high smoothness and gloss. This ink-receiving layer is formed in a multi-layered structure and has an uppermost gloss layer comprising, as a principal component, colloidal particles or composite colloidal particles, and laminated on an ink-fixing layer. The uppermost gloss layer is formed by pressing the uppermost layer in a wetted condition against a mirror-finished perperal surface of a shaping roll. However, the uppermost layer laminated on the ink-fixing layer easily sinks into the ink-fixing layer upon pressing and thus is difficult to sufficiently smooth by the mirror surface-transfer method. Accordingly, to enhance the mirror surface-transfer effect onto the uppermost layer, a polymer latex is used as a binder for the formation of the uppermost gloss layer. The use of the polymer latex causes the resultant uppermost gloss layer to be easily and finely cracked. The fine cracks contribute to enhancing the ink absorption rate in the uppermost gloss layer. However, the fine cracks also cause the resultant uppermost gloss layer to exhibit a reduced gloss and the ink dots formed on the uppermost gloss layer to have jagged circumferences and to be easily connected to each other. These features of the ink dots result in reduced clarity and sharpness of the printed ink images.
Further, in the above-mentioned ink jet recording material, since the uppermost layer of the ink-receiving layer is smoothed by a mirror-finished surface, and then dried, the substrate must be an air-permeable sheet, for example, a paper sheet. A non-permeable, high smoothness sheet, for example, a plastic film or a laminate, cannot be used as the substrate. When a paper sheet having a rough surface is used as a substrate, the resultant ink-receiving layer has a rough surface derived from the paper sheet surface. Also, when the recording sheet is dried water vapor permeates through the ink-receiving layer and forms pinholes in the ink-receiving layer. Therefore, the ink-receiving layer having a high gloss similar to that of photographic printing sheets is difficult to obtain.
To solve the above-mentioned problems, the inventors of the present invention have provided an ink jet recording material produced by forming an ink-receiving layer on a surface of a shaping base; bonding a substrate to the ink-receiving layer formed on the shaping base through an intermediate layer comprising a bonding material or an adhesive material; and separating the resultant laminate from the shaping base. In this type of ink jet recording material, a water-soluble resin can be used as a binder of the ink-receiving layer, the resultant ink dots on the ink-receiving layer is in the form of a true circle and the ink-receiving layer exhibits a high smoothness, a high ink absorption and a high gloss.
However, where the ink-receiving layer is formed in two or more-layered structure on the shaping base surface, a first layer (corresponding to an porous uppermost layer of the resultant ink jet recording is formed on the sheet) shaping base surface and then second, third and other layers are successively formed on the porous uppermost layer. In this case, pores or voids may be formed in the surface portions of the second, third or other layers, and may be retained even after the resultant multi-layered ink-receiving layer is transferred from the shaping base to the substrate surface. Also, when the coating liquids for the second, third and other layers are successively coated on the uppermost layer, the binder contained in those layers may diffuse into the first layer (porous uppermost layer) so as to change the ink-absorbing property of the first layer (porous uppermost layer). Further, as the amounts of the second, third and other layers are increased, the resultant multi-layered ink-receiving layer may exhibit a poor resistance to crack-formation.
U.S. Pat. No. 5,612,281 for Kobayashi et al discloses a recording sheet for ink jet recording having a transparent support and transparent colorant-receptive layer having a three dimensional network structure formed from silicic anhydride particles and a water-soluble resin. The coating solution for the colorant-receptive layer is prepared by, for example, by adding silica fine particles having an average primary particle size (diameter) of not more than 10 nm to water, dispersing the fine silica particles by using a high speed rotary wet colloid mill, adding, to the resultant aqueous fine silica dispersion,.an aqueous polyvinyl alcohol solution and adjusting the pH of the resultant aqueous dispersion to 4.5, to obtain a homogeneous sol. The coating solution is coated on the transparent support and dried to provide the colorant-receptive layer. When the coating solution layer is dried on the transparent support and reaches a gelation concentration through the evaporation of water, a wet gel is formed and, as the drying further progresses, a porous xerogel is formed to obtain a colorant receptive layer. In the resultant colorant receptive layer, the fine silica anhydride particles having a primary particle size of not more than 10 nm are adhered to each other through the polyvinyl alcohol binder to form a network structure, but not secondary particles each consisting of a plurality of primary particles agglomerated with each other, of the fine silica particles. Thus, the colorant receptive layer has a relatively high density and exhibits a poor ink absorbing property. The silica really disclosed in the U.S. patent is only dry method silica (dry process silica). The dry method silica causes the resultant ink-receiving layer to exhibit an ink absorbing property lower than that of the wet method silica (wet process silica).
An object of the present invention is to provide an ink jet recording material having a high gloss, a high resistance to weathering and a high resistance to water and capable of recording ink images having excellent clarity, and sharpness and satisfactory color density, brightness and brilliancy.
The above-mentioned object can be attained by the ink jet recording material of the present invention which comprises:
a substrate; and
an ink-receiving layer formed on at least one surface of the substrate, wherein said ink-receiving layer comprises a binder, and a plurality of secondary particles, wherein said secondary particles have an average secondary particle size of 10 to 300 nm, each of said secondary particles consisting essentially of a plurality of primary particles of at least one member selected from the group consisting of silica prepared by wet method, which silica will be referred to as wet method silica hereinafter, and aluminosilicate, and wherein said primary particles are agglomerated with each other to form said secondary particles without any binder, in each of the secondary particles, pores being formed between the agglomerated primary particles.
In an embodiment of the ink jet recording material of the present invention, the ink-receiving layer has a haze value of 4 to 65%.
In another embodiment of the ink jet recording material of the present invention, the ink-receiving layer has a plurality of pores formed therein and exhibits a pore radius distribution curve having a peak-corresponding to a pore radius of about 40 nm or less.
The process of the present invention for producing the ink jet recording material comprises the steps of:
forming an ink-receiving layer comprising a binder, and a plurality of secondary particles, having an average secondary particle size of 500 nm or less and each comprising a plurality of primary particles of at least one member selected from the group consisting of silica and aluminosilicate, and agglomerated with each other to form the secondary particles, on a surface of a shaping base;
bonding the substrate to the ink-receiving layer provided on the shaping base to form a laminate; and
separating the resultant laminate from the shaping base.